(1) Field of the Invention
The present invention relates to a process for growing heteroepitaxial single crystal diamond and diamond crystallite precursors. In particular, the present invention uses a surface on a metal oxide substrate coated with a thin film of iridium which enables growing the single crystal diamond or the diamond nuclei as precursors.
(2) Description of Related Art
FCC (face-centered cubic) Ir buffer layers have been used as substrates for single crystal diamond film growth by low pressure chemical vapor deposition (CVD). MgO and SrTiO3 were used as substrates for (001) Ir films (Ohtsuka, K., et al., Jpn. J. Appl. Phys. 36, 1214 (1997); Schreck, M., et al., Appl. Phys. Lett. 74 650 (1999); and Tsubota, T., et al., Diamond and Related Materials 9 1380 (2000)). Cubic MgO (Ohtsuka, K., et al., Jpn. J. Appl. Phys. 36, 1214 (1997); and Tsubota, T., et al., Diamond and Related Materials 9 1380 (2000)) and SrTiO3 (Schreck, H., et al., Appl. Phys. Lett. 74 650 (1999); Hörmann, et al., Diamond and Related Materials 9 256 (2000); and Dai, Z., et al., Proc. Mat. Res. Soc., P11.35, 684 (2001)).
Heteroepitaxial growth of advanced electronic materials depends on the development of suitable, relatively low-cost, lattice-matched substrate systems. Initial attempts toward heteroepitaxy of diamond were made with growth of highly-oriented crystallites of diamond on silicon, despite the existence of a large lattice parameter mismatch (Walter, S., et al. Appl. Phys. Lett. 62 1215 (1993); Jiang, X, Diamond and Related Materials 2 1112 (1993); and Wild, C., et al., Diamond and Related Materials 3 373 (1994)). It was later found that films of Ir, grown as a buffer layer on MgO, could serve as a substrate for the nucleation and growth of CVD diamond (Ohtsuka, K., et al., Jpn. J. Appl. Phys. Pt. 2 35 (1996) L1072); Ohtsuka, K., et al., Jpn. J. Appl. Phys. Pt. 2 36 (1997) L1214; and Tsubota, T., et al., Diamond and Related Materials 9 1380 (2000)). With a lattice parameter 7% larger than diamond, Ir appears to have sufficient long-term chemical and physical stability in the high-temperature environment of a hydrogen plasma. The use of SrTiO3 as a replacement for MgO has also proven useful in decreasing the mosaic spread of the epitaxial Ir and the resultant heteroepitaxial diamond (Schreck, M., et al., Appl. Phys. Lett. 74 650 (1999); and Schreck, M., et al., Appl. Phys. Lett. 78 192 (2001)).
In parallel with heteroepitaxial growth efforts, the conditions for achieving high diamond nucleation densities on various substrates have been extensively examined. The bias-enhanced nucleation process (Yugo, S., et al., Appl. Phys. Lett. 58 1036 (1991)), in which a negative voltage applied to the substrate results in its bombardment by relatively low-energy positive ions extracted from the plasma, is a key step for inducing the formation of diamond nuclei. It is important that the nuclei adopt the underlying orientation of the substrate and that their density be maximized so as to lead to rapid coalescence of crystallites during the early stages of growth. Although the conditions that lead to effective nucleation are well known in principle, there is little agreement on the physical mechanisms that underpin the process. The process is also system-specific to some degree, depending on details of reactor geometry and a multitude of processing parameters.
Single crystal diamond is particularly useful in the electronics and acoustics fields. U.S. Pat. No. 5,397,428 to Stoner et al; U.S. Pat. No. 5,587,210 to Marchywka et al; U.S. Pat. No. 5,743,957 to Kobashi; U.S. Pat. No. 5,863,324 to Kobashi et al; U.S. Pat. No. 5,891,575 to Marchywka et al; U.S. Pat. No. 5,993,919 to Tsuno et al; U.S. Pat. No. 6,032,611 to Asakawa et al; U.S. Pat. No. 6,063,187 to Lee et al; U.S. Pat. No. 6,080,378 to Yokota et al; U.S. Pat. No. 6,096,129 to Saito et al; and U.S. Pat. No. 6,383,288 to Hayashi et al; are relevant to the present invention and form part of the background for the invention. The disclosure of U.S. Pat. No. 5,397,428 to Stoner et al and U.S. Pat. No. 5,993,919 to Tsuno et al is incorporated by reference for its general disclosure.